A high-selective filter is a crucial component in wired and wireless communication systems, because they control the usage of frequency spectrum there. Due to a close proximity of the operation frequency band of functional elements in a device, the frequency characteristics skirt of the filter applied has to be sharp.
However, providing such electrical performance is a complex problem in high-density and multifunctional devices, because additional resonant elements are required.
Moreover, the use of such additional elements, which can improve the filter skirt sharpness, can lead to the increase of the in-band insertion losses that can be unac-ceptable for real applications.
Japanese Patent JP4367660 (U.S. Pat. No. 7,705,695B2) discloses composite via structures and filters based on these structures, which are formed in multilayer substrates. Compactness of resonant elements in these structures is provided by conductive plates connected to the signal via forming in such way an artificial dielectric of a high permittivity.
PCT Laid Open Patent Publication WO 2010/073410 discloses via structures and filters based on these via structures, in which an artificial dielectric of a high permittivity is formed by corrugated conductive plates connected to the signal via.
PCT Laid Open Patent Publication WO/2011/010393 discloses resonant elements and filters based on these elements, in which an artificial dielectric is formed by double corrugated surface obtained by the corrugation of both the signal plates and ground plates.
Above-mentioned structures are miniature and cost-effective ones. However, it is important to provide such type of resonators in a filter which can improve its selectivity.